Real-time multimedia conferencing services have typically been provided by connecting signals over circuit-switched networks, such as an Integrated Services Digital Network (ISDN), having guaranteed quality of service (QOS). Although circuit-switched networks provide a guarantee of QOS as they provide a communications channel for exclusive use by connected parties until the connection is released, they cannot save bandwidth through statistical multiplexing (i.e., by dynamically allocating bandwidth according to actual demand rather than on a predefined basis). Therefore, the adoption of multimedia services through the interconnection of geographically dispersed locations over circuit-switched networks is very limited because it is cost prohibitive.
Accordingly, millions of multimedia personal computers (MPCs) or workstations throughout the world are connected to packet-switched "nonguaranteed" quality of service local area networks such as Ethernet (EN), Token Ring (TN), or Fiber Distributed Data Interface (FDDI). By definition of the protocol standards for each of EN, TN and FDDI, for example, the LANs are "nonguaranteed" in that there is no guarantee of performance in providing services through that network. Such networks are inherently unreliable as they provide no guarantee of bandwidth or quality of service parameters. Real-time multimedia conferencing services require a guarantee of bandwidth and quality of service parameters. A critical requirement for successful real-time conferencing is to ensure that there are sufficient network and bridging resources available to maintain the desired level of performance once the conference call has been accepted. However, in a conventional system the bridge has absolutely no knowledge of the state of the network and its resources.
Recently, the ATM network has emerged as the most promising networking technology for providing statistical multiplexing of real-time isochronous signals (i.e., signals repeating in time, such as 8khz voice samples for example), such as audio and video, as well as asynchronous signals, such as data, while maintaining a guarantee of quality of service for each signal.